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Abstract Azo dyes with electron-donating and neutral substituents in PMMA matrix and solution were prepared and characterized. High optical quality films were made for linear optical characterization of azo dyes. Two-photon absorption spectra, for investigated compounds dissolved in DMF, were obtained by Z-Scan measurements. The π-π* transition of investigated compounds is significantly red-shifted and overlaps with n-π* transition. Accordingly azo dye with electron-donating group is more red-shifted compared to molecule with neutral group. Refractive index and efficiency of two-photon absorption cross-section for azo dye with neutral substituent is lower compared to azo dye with electron-donating substituent. [ABSTRACT FROM AUTHOR]

Three novel tyrosine-conjugated azobenzene molecules were designed and their ability to target a natural chiral host matrix (human serum albumin, HSA) was investigated. We found that the interplay between the spatial configuration of the chiral substituents and the change in local symmetry resulting from the photoisomerization process strongly affects the optical activity of the bound photochromes. In particular, the different signal amplification obtained upon binding of the photoswitches to the biopolymer enables obtaining a chirooptical system tunable over a wide range of wavelengths. [ABSTRACT FROM AUTHOR]

Non-viral vectors for gene therapy such as DNA-cationic probe complexes offer important bio-safety advantages over viral approaches, due to their reduced pathogenicity, immunogenicity and cytotoxicity. In the present study we examine two polycationic water-soluble azobenzene derivatives (bis-Azo-2N and bis-Azo-3N) containing different linear unsubstituted polyamine moieties and we demonstrate the ability of such photochromes to destabilize the intrinsic B-DNA secondary structure in a concentration-dependent manner. Furthermore, through a detailed series of biophysical experiments, varying the photochrome conformation, temperature, salt and DNA concentration, we provide a detailed insight into the azobenzene–DNA binding pathway (Ka: bis-Azo-2N(trans)-DNA = 5.3 ± 0.3 × 104 M−1, Ka: bis-Azo-2N(cis)-DNA = 2.6 ± 0.2 × 104 M−1, Ka: bis-Azo-3N(trans)-DNA = 7.1 ± 0.4 × 104 M−1 and Ka: bis-Azo-3N(cis)-DNA = 5.1 ± 0.4 × 104 M−1) establishing the versatility of such materials as promising candidates for use in non-viral gene delivery systems. [ABSTRACT FROM AUTHOR]

Cetyltrimethylammonium bromide (CTAB) and (11-mercaptoundecyl)tetra(ethylene glycol) (PEG-SH) capped gold nanorods were prepared and dispersed in water and dimethyl sulfoxide (DMSO). Transmission electron microscopy images reveal that changing the solvent from water to DMSO cause that nanoparticles tend to organize (PEG-SH ligand) or aggregate (CTAB ligand). UV-vis absorbance spectra reveal that ligand as well as solvent exchange cause positive solvatochromic shifts and changes in the relative extinction values. After the transfer of nanorods from a solvent of lower to higher refraction index a red shift of the longitudinal surface plasmon resonance band is observed. This effect is more pronounced in the case of PEG-SH capped nanorods. Time resolved pump-probe measurements revealed that both ligand and solvent exchange influence the excited state relaxation times, however, a more pronounced change is induced by the ligand exchange. Two-photon excited fluorescence spectra of PEG-SH covered nanorods showed a slight intensity increase when moving from water to DMSO solvent. [ABSTRACT FROM AUTHOR]

Amyloid fibrils are excellent self-assembling nanotemplates for organic molecules such as dyes. Here, we demonstrate that laser dye-doped lysozyme type fibrils exhibit significantly reduced threshold for stimulated emission compared to that observed in usual matrices. Laser action was studied in slab planar waveguides of the amyloids doped with Stilbene 420 laser dye prepared using a film casting technique. The lowering of the threshold of stimulated emission is analyzed in the context of intrinsic structure of the amyloid nanotemplates, electrostatic interaction of different microstructures with dye molecules, as well as material properties of the cast layers. All these factors are considered to be of importance for introducing gain for random laser operation. [ABSTRACT FROM AUTHOR]

We investigate the photophysical and amplified spontaneous emission properties of a series of monodisperse solution-processable oligofluorenes functionalized with hexyl chains at the C9 position of each fluorene unit. Thin films of these oligofluorenes are then used in organic field-effect transistors and their charge transport properties are examined. We have particularly focused our attention on the influence of oligofluorene length on the absorption and steady-state fluorescence spectra, on the HOMO/LUMO energy levels, on the photoluminescence lifetime and quantum yield as well as on the amplified spontaneous emission properties and the charge carrier mobilities. Differential scanning calorimetry and X-ray diffraction measurements demonstrate that, among all oligofluorene derivatives used in this study, only the structure and morphology of the pentafluorene film is significantly modified by a thermal treatment above the glass transition temperature, resulting in a 9 nm blue-shift of the fluorescence spectrum without significant changes in the photoluminescence quantum yield and in the amplified spontaneous emission threshold. In parallel, hole field-effect mobility is significantly increased from 8.6 × 10−7 to 3.8 × 10−5 cm2 V−1 s−1 upon thermal treatment, due to an increase of crystallinity. This study provides useful insights into the morphological control of oligofluorene thin films and how it affects their photophysical and charge transport properties. Moreover, we provide evidence that, because of the low threshold, the tunability of the amplified spontaneous emission and the photostability of the films, these oligofluorenes are promising candidates for organic solid-state laser applications. [ABSTRACT FROM AUTHOR]

Nonlinear refraction and nonlinear absorption in stoichiometric colloidal CuInS2 quantum dots, with absorption edge tuned up to the visible spectral region, were investigated. The nonlinear optical response of the quantum dots was measured in a wide range of wavelengths (700-1600 nm) using the Z-scan technique. The measurements revealed the presence of two-photon absorption in the near-infrared range and the negative nonlinear refraction in almost whole spectral range for all the investigated nanoparticles. The cubic nonlinearity of CuInS2 quantum dots is discussed in terms of defect-related optical properties of the material. The results indicate that CuInS2 quantum dots may be an interesting material for the single and multiphoton luminescence bio-detection techniques. [ABSTRACT FROM AUTHOR]

Hybrid field-effect transistors (FETs) based on poly(3-hexylthiophene) (P3HT) containing CdSe quantum dots (QDs) were fabricated. The effect of the concentration of QDs on charge transport in the hybrid material was studied. The influence of the QDs capping ligand on charge transport parameters was investigated by replacing the conventional trioctylphosphine oxide (TOPO) surfactant with pyridine to provide closer contact between the organic and inorganic components. Electrical parameters of FETs with an active layer made of P3HT:CdSe QDs blend were determined, showing field-effect hole mobilities up to 1.1×10 cm/Vs. Incorporation of TOPO covered CdSe QDs decreased the charge carrier mobility while the pyridine covered CdSe QDs did not alter this transport parameter significantly. [ABSTRACT FROM AUTHOR]

Nonlinear absorption and nonlinear refraction of colloidal CdSe quantum dots (QDs) of two sizes were investigated in a wide spectral range with the Z-scan technique using a tunable femtosecond laser system. The nonlinear absorption was found to be the strongest close to twice the wavelength of the second exciton absorption band of the QDs. Based on nonlinear optical parameters the exciton binding energy has been determined. The current results are compared to the nonlinear properties of CdSe QDs presented in the literature. The features of this system relevant for multiphoton fluorescence microscopy applications are discussed. [ABSTRACT FROM AUTHOR]

We investigated linear optical and second-order nonlinear optical (NLO) properties of films of poly(bisphenol A carbonate) resin, and a newly synthesised titania/silica/hybrid sol-gel polymer resin doped with Disperse Red 1 (DR1) molecular chromophore. DC electric field induced second harmonic generation (SHG) technique has been used to monitor in situ the polar alignment and relaxation of orientation of the guest molecules in the corona-poled films. The temporal behaviour of the second harmonic signal was remarkably different in these two polymers both during poling and when the poling field was turned off. A fast decay of the second harmonic intensity was observed at room temperature in 3 wt% DR1-doped sol-gel film, and a long relaxation time constant was found in 13 wt% DR1-doped polycarbonate film. Resonantly enhanced d eff coefficient of about 9 pm/V was found in the sol-gel film, and 25 pm/V in the polycarbonate film at the fundamental wavelength 1053 nm. The d 33 values were about 20 pm/V, and 60 pm/V in these films, respectively. The SHG results were used to estimate the average rotation mobility parameter of DR1 molecules in the host polymers. [ABSTRACT FROM AUTHOR]

Highly oxygen-rich SiOx thin films were prepared using a helicon plasma activated reactive evaporation technique. A small second-order optical nonlinearity was observed in the as-grown films, and thermal poling induced nonlinearity in the films was found to be much larger than that in stoichiometric SiO2 films. These phenomena were associated with the non-impurity defects in the oxygen-rich films. [ABSTRACT FROM AUTHOR]

We report Bragg grating structures fabricated by focused ion beam milling in optical waveguides, and demonstrate that they can be used as a powerful diagnostic of optical modes in very high index waveguides. We show that higher-order lossy modes, which can be present in large numbers even in single-moded silicon-on-insulator waveguides, can dramatically affect the optical transmission spectra of Bragg gratings in these waveguides, even though these modes are normally not observable. Our results not only illuminate challenges to realize practical gratings in high index waveguides, but raise the possibility of devices based on mode conversion to extremely high order modes. [ABSTRACT FROM AUTHOR]

Investigates the optically stimulated birefringence and dichroism by combining heterodyned detection of phase-tuned optical Kerr gate (OKG) signal. Determination of the real and imaginary parts of complex third-order optical nonlinearity; Value of the pulse used on tetrahydrofuran solutions of canthaxanthin; Advantage of the heterodyned OKG detection method.